ContentTypeParser
Content-Type
Parser
Natively, Fastify only supports 'application/json'
and 'text/plain'
content
types. If the content type is not one of these, an
FST_ERR_CTP_INVALID_MEDIA_TYPE
error will be thrown.
Other common content types are supported through the use of
plugins.
The default charset is utf-8
. If you need to support different content types,
you can use the addContentTypeParser
API. The default JSON and/or plain text
parser can be changed or removed.
Note: If you decide to specify your own content type with the Content-Type
header, UTF-8 will not be the default. Be sure to include UTF-8 like this
text/html; charset=utf-8
.
As with the other APIs, addContentTypeParser
is encapsulated in the scope in
which it is declared. This means that if you declare it in the root scope it
will be available everywhere, while if you declare it inside a plugin it will be
available only in that scope and its children.
Fastify automatically adds the parsed request payload to the Fastify
request object which you can access with request.body
.
Note that for GET
and HEAD
requests the payload is never parsed. For
OPTIONS
and DELETE
requests the payload is only parsed if the content type
is given in the content-type header. If it is not given, the
catch-all parser is not executed as with POST
, PUT
and
PATCH
, but the payload is simply not parsed.
⚠ Security Notice
When using with RegExp to detect
Content-Type
, you should beware of how to properly detect theContent-Type
. For example, if you needapplication/*
, you should use/^application\/([\w-]+);?/
to match the essence MIME type only.
Usage
fastify.addContentTypeParser('application/jsoff', function (request, payload, done) {
jsoffParser(payload, function (err, body) {
done(err, body)
})
})
// Handle multiple content types with the same function
fastify.addContentTypeParser(['text/xml', 'application/xml'], function (request, payload, done) {
xmlParser(payload, function (err, body) {
done(err, body)
})
})
// Async is also supported in Node versions >= 8.0.0
fastify.addContentTypeParser('application/jsoff', async function (request, payload) {
const res = await jsoffParserAsync(payload)
return res
})
// Handle all content types that matches RegExp
fastify.addContentTypeParser(/^image\/([\w-]+);?/, function (request, payload, done) {
imageParser(payload, function (err, body) {
done(err, body)
})
})
// Can use default JSON/Text parser for different content Types
fastify.addContentTypeParser('text/json', { parseAs: 'string' }, fastify.getDefaultJsonParser('ignore', 'ignore'))
Fastify first tries to match a content-type parser with a string
value before
trying to find a matching RegExp
. If you provide overlapping content types,
Fastify tries to find a matching content type by starting with the last one
passed and ending with the first one. So if you want to specify a general
content type more precisely, first specify the general content type and then the
more specific one, like in the example below.
// Here only the second content type parser is called because its value also matches the first one
fastify.addContentTypeParser('application/vnd.custom+xml', (request, body, done) => {} )
fastify.addContentTypeParser('application/vnd.custom', (request, body, done) => {} )
// Here the desired behavior is achieved because fastify first tries to match the
// `application/vnd.custom+xml` content type parser
fastify.addContentTypeParser('application/vnd.custom', (request, body, done) => {} )
fastify.addContentTypeParser('application/vnd.custom+xml', (request, body, done) => {} )
Using addContentTypeParser with fastify.register
When using addContentTypeParser
in combination with fastify.register
,
await
should not be used when registering routes. Using await
causes
the route registration to be asynchronous and can lead to routes being registered
before the addContentTypeParser has been set.
Correct Usage
const fastify = require('fastify')();
fastify.register((fastify, opts) => {
fastify.addContentTypeParser('application/json', function (request, payload, done) {
jsonParser(payload, function (err, body) {
done(err, body)
})
})
fastify.get('/hello', async (req, res) => {});
});
Besides the addContentTypeParser
API there are further APIs that can be used.
These are hasContentTypeParser
, removeContentTypeParser
and
removeAllContentTypeParsers
.
hasContentTypeParser
You can use the hasContentTypeParser
API to find if a specific content type
parser already exists.
if (!fastify.hasContentTypeParser('application/jsoff')){
fastify.addContentTypeParser('application/jsoff', function (request, payload, done) {
jsoffParser(payload, function (err, body) {
done(err, body)
})
})
}
removeContentTypeParser
With removeContentTypeParser
a single or an array of content types can be
removed. The method supports string
and RegExp
content types.
fastify.addContentTypeParser('text/xml', function (request, payload, done) {
xmlParser(payload, function (err, body) {
done(err, body)
})
})
// Removes the both built-in content type parsers so that only the content type parser for text/html is available
fastify.removeContentTypeParser(['application/json', 'text/plain'])
removeAllContentTypeParsers
In the example from just above, it is noticeable that we need to specify each
content type that we want to remove. To solve this problem Fastify provides the
removeAllContentTypeParsers
API. This can be used to remove all currently
existing content type parsers. In the example below we achieve the same as in
the example above except that we do not need to specify each content type to
delete. Just like removeContentTypeParser
, this API supports encapsulation.
The API is especially useful if you want to register a catch-all content type
parser that should be executed for every content type and the
built-in parsers should be ignored as well.
fastify.removeAllContentTypeParsers()
fastify.addContentTypeParser('text/xml', function (request, payload, done) {
xmlParser(payload, function (err, body) {
done(err, body)
})
})
Notice: The old syntaxes function(req, done)
and async function(req)
for
the parser are still supported but they are deprecated.
Body Parser
You can parse the body of a request in two ways. The first one is shown above:
you add a custom content type parser and handle the request stream. In the
second one, you should pass a parseAs
option to the addContentTypeParser
API, where you declare how you want to get the body. It could be of type
'string'
or 'buffer'
. If you use the parseAs
option, Fastify will
internally handle the stream and perform some checks, such as the maximum
size of the body and the content length. If the
limit is exceeded the custom parser will not be invoked.
fastify.addContentTypeParser('application/json', { parseAs: 'string' }, function (req, body, done) {
try {
const json = JSON.parse(body)
done(null, json)
} catch (err) {
err.statusCode = 400
done(err, undefined)
}
})
See
example/parser.js
for an example.
Custom Parser Options
parseAs
(string): Either'string'
or'buffer'
to designate how the incoming data should be collected. Default:'buffer'
.bodyLimit
(number): The maximum payload size, in bytes, that the custom parser will accept. Defaults to the global body limit passed to theFastify factory function
.
Catch-All
There are some cases where you need to catch all requests regardless of their
content type. With Fastify, you can just use the '*'
content type.
fastify.addContentTypeParser('*', function (request, payload, done) {
let data = ''
payload.on('data', chunk => { data += chunk })
payload.on('end', () => {
done(null, data)
})
})
Using this, all requests that do not have a corresponding content type parser will be handled by the specified function.
This is also useful for piping the request stream. You can define a content parser like:
fastify.addContentTypeParser('*', function (request, payload, done) {
done()
})
and then access the core HTTP request directly for piping it where you want:
app.post('/hello', (request, reply) => {
reply.send(request.raw)
})
Here is a complete example that logs incoming json line objects:
const split2 = require('split2')
const pump = require('pump')
fastify.addContentTypeParser('*', (request, payload, done) => {
done(null, pump(payload, split2(JSON.parse)))
})
fastify.route({
method: 'POST',
url: '/api/log/jsons',
handler: (req, res) => {
req.body.on('data', d => console.log(d)) // log every incoming object
}
})
For piping file uploads you may want to check out this plugin.
If you want the content type parser to be executed on all content types and not
only on those that don't have a specific one, you should call the
removeAllContentTypeParsers
method first.
// Without this call, the request body with the content type application/json would be processed by the built-in JSON parser
fastify.removeAllContentTypeParsers()
fastify.addContentTypeParser('*', function (request, payload, done) {
const data = ''
payload.on('data', chunk => { data += chunk })
payload.on('end', () => {
done(null, data)
})
})